In my search to find cost effective I/O modules I came across ControlByWeb Ethernet I/O the other day. The product line is impressive and they’re reasonably priced. There’s digital input, analog input, temperature input, and relay outputs. Some have advanced features such as SNMP support, but at the bare minimum they all support HTTP/XML and Modbus/TCP. The devices can also interface with each other directly and several even have a 802.11af POE powered version. I’ll probably end up using modbus since I already have some RS-485 modbus stuff in place.
My first planned project for these Ethernet I/O modules is to monitor a multistage cooling system; things like thermostat stage calls compared to compressor calls since there’s an economizer in the mix that modifies the true compressor staging calls.